The continued evolution of computer and optical technologies has resulted in increasing demands for chemically clean and particulate-free surfaces and, hence, a rapid and effective means for producing them. For example, as computer technology continues to rely on state-of-the-art microelectronics, and microelectronic devices continue to shrink in size, computer technology has become increasingly vulnerable to chemical and particulate contaminants. Particles from "clean" rooms and processing equipment are increasingly a significant problem. See generally "Device Materials and Processing Beyond VHSIC," by Bowling et al., August 1987, a report prepared for the Defense Advanced Research Project Agency of the Office of Naval Research, Arlington, Va.
Amorphous thin film structures are used in a variety of industrial applications including the manufacture of semiconductor and optical components, magnetic disk storage media, wear and corrosion resistant coating materials, industrial plating, solar cells, thin film transistors and reflection control coatings for transmissive and reflective optical elements. However, such thin film structures are also adversely affected by the presence of microparticulates, chemical residues and metallic debris on base layers. Such contaminants impede the growth, adhesion, wear resistance and stability of the thin films in these applications.
Conventional methods for cleaning single crystalline and amorphous surfaces include in-vacuum cleavage, in-vacuum evaporation, chemical etching and electron beam scrubbing. None of these has proven entirely satisfactory. See e.g., U.S. Pat. No. 4,292,093 to Ownby et al. and "Preparation of Atomically Clean Silicon Surfaces by Pulsed Laser Irradiation," by D. M. Zehner et al., Appl. Phys. Lett. 36 (1), Jan. 1, 1980, pp. 56-59. Moreover, chemical etching techniques utilize materials such as hydrofluoric, sulfuric, nitric and other strong acids and organic solvents such as trichloroethane and various complexing agents. These materials are plainly hazardous and subject to environmental concerns.
More recently, others have investigated the use of lasers to clean such surfaces. The laser methods disclosed to date invariably rely on the transmission of sufficient energy to induce thermal melting and recrystallization at the subject surface. These include, for example, ruby lasers ("Preparation of Atomically Clean Silicon Surface by Pulsed Laser irradiation," by Zehner et al., supra), Q-switched ruby lasers ("Laser Cleaning of GaAs Surfaces in Vacuo," Rodway et al., Appl. of Surface Science, 6, 1980, pp. 76-81), Nd-YAG lasers (U.S. Pat. No. 4,292,093 to Ownby et al.) and argon-ion lasers ("Effect of Low Intensity Laser Radiation During Oxidation of the GaAs (110) Surface, " Petro et al., J. Vac. Sci. Technol., 21(2), July/August 1982, pp. 405-408) and KrF excimer lasers ("Excimer-laser Gas-assisted Deposition of Crystalline and Amorphous Films," Reddy, J. Opt. Soc. Amer. B, 3(5), May 1986).
As yet, however, such laser-based cleaning methods are still too slow or too ineffective to enable their use in a commercially viable cleaning process. Laser annealing also tends to introduce point defects, and enhances cracking and other irregularities at the substrate surface and thin film/substrate interface. In addition, impurities or microparticulates residing on the surface are not actually removed by these processes, but rather incorporated into the molten surface layer, producing localized doping and secondary defect nucleation.
Accordingly, it is an object of this invention to provide a novel method for cleaning surfaces. More particularly, it is an object of the invention to provide a rapid and effective method for removing chemical and metallic impurities and particulate debris from surfaces. It is still another object of the invention to provide a method for removing such impurities and debris from surfaces without the use of toxic or hazardous chemicals and without imparting substantial chemical or physical change to the surface.
It is a further object of the invention to provide a rapid and effective method for removing such impurities and debris from essentially single crystalline and amorphous materials used to make microelectronic devices, optical components, magnetic disk storage media, solar cells, thin film transistors and such other devices as described earlier without degrading the surface. It is still another object of the invention to provide a novel method for removing elemental impurities such as carbon, oxygen, sodium, calcium, potassium, magnesium and the like from such surfaces.